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Using miniature cuboidal specimens to determine compression Stress–strain curve of sheet metal under static and dynamic loading
No full textInternational audienceCharacterizing the stress-strain response of sheet metal under both tension and compression is important to provide accurate predictions of spring-back in sheet metal forming. Data on compression is scarce as antibuckling devices typically need to be used to attain large strains in compression experiments on sheet metal. As a technically simpler alternative, we propose upsetting experiments with miniature cuboidal specimens as these can be conveniently extracted from sheet metal. In addition to static experiments, we design a Dropkinson bar system for the dynamic compression testing of miniature specimens. We demonstrate through finite element simulations that upsetting specimens with square cross-section are equally-suitable for measuring the stress-strain curve as traditional cylindrical specimens with circular cross-sections. Even though the local surface strains can be conveniently measured with planar DIC, detailed analysis revealed that using the average strain along the full specimen height yields the most accurate stress-strain curve estimation. Static and dynamic demonstration experiments are performed on miniature cuboidal specimens extracted from DP780, DP980 and DP1180 steel sheets. The comparison with the results from uniaxial tension experiments reveals a systematic strength differential effect with a yield stress for compression that is up to 4% higher than that for tension. The dynamic experiments at strain rates of about 750/s suggest a yield strength increase of up to 25% (as compared to static experiments)
Dual-functional hybrid layered double hydroxide-based material for enhanced energy storage and photocatalytic activity
No full textInternational audienceIn the search for suitable materials for both energy storage and environmental applications, this work synthesizes a ternary nanocomposite comprises of nickel-cobalt layered double hydroxide (NiCo LDH), manganese dioxide (MnO2), and multi-walled carbon nanotubes (MWCNT) via a facile single pot hydrothermal technique. The hybrid nanocomposite is evaluated as an electrode material for supercapacitors and as a photocatalyst material for photocatalytic drug degradation. Various physicochemical characterization techniques were performed to study the formation of the NiCo LDH/MnO2/MWCNT nanocomposite. The electrode exhibits a high specific capacitance of 2178 F/g at 1 A/g, with 87 % of capacitance retention after 5000 GCD cycles. A hybrid supercapacitor (HSC) was assembled using activated carbon (AC) as the negative electrode and the as-prepared ternary nanocomposite as the positive electrode in 3M KOH aqueous electrolyte. The device achieves a high specific capacitance of 235 F/g, a specific energy of 76 Wh/kg, and 98.2 % coulombic efficiency after 10,000 cycles. The enhanced electrochemical performance is attributed to synergistic interactions between MWCNT, NiCo LDH, and MnO2, improving charge transfer kinetics and redox activity. Additionally, the nanocomposite demonstrates 91.2 % degradation efficiency in the degradation of tetracycline drug under UV–visible light, due to improved light absorption and reduced charge recombination. These results highlight the potential of the NiCo LDH/MnO2/MWCNT nanocomposite for energy and environmental applications
Cast number 1740 "Caverne de Baye" trepaned skull, La Plata Museum. When one skull can hide another!
No full texthttps://scicomove.hypotheses.org/5080Investigation into a trepanned skull from the La Plata Museum in Argentina
Towards the digital twin of a multi-stage forming process for metallic sheets
No full textInternational audienceDigital twins are a major constituent of advanced and smart manufacturing, to decrease the time tomarket, improve process efficiency and reduce waste production. There seems to be a common unders-tanding on the different levels of integration of the communication between the physical object and thedigital object, i.e., digital model, shadow and twin, with the digital twin being the stage when it sendsactions to perform in real-time to the physical object, for an efficient execution of the process. In thefield of material forming, digital models are well established nowadays, based on finite element simula-tions and physics-based constitutive equations to represent the material mechanical behavior, althoughin general the high calculation time prevents any real-time interaction. The aim of this study is to designfirst a digital shadow of a progressive multi-step sheet forming process, aiming at a digital twin in asecond step. The target is to adjust the process parameters according to the mechanical properties va-riations. The physical process involves cutting of rectangular blanks, U-draw bending, springback anda last calibration stage to compensate for the springback. To provide a reliable representation of themechanical behavior under complex stress states and large strains, distortional hardening is consideredalong with isotropic hardening. An analysis of variations of the mechanical properties of DP600 steelwas performed, to generate several material parameter sets. Based on finite element simulations of themulti-step process, a sensitivity analysis of the forming process outputs to the mechanical propertiesvariations is carried out. The results highlight the operating principle of the digital twin, stressing outthe required sensors
Formulation hyperbolique de l'endommagement à gradient pour la simulation par volumes finis de la rupture fragile dynamique
No full textInternational audienceIn this work, a new hyperbolic gradient damage model for the numerical simulation of dynamic brittlefracture problems is presented. The derivation follows from the application of the “extended Lagran-gian” method and allows to replace the global optimization problem usually solved for damage evolu-tion with a set of purely local equations that can easily be treated using finite volumes. The unilateraleffects are here introduced in a spherical/deviatoric additive split of the elastic energy that ensureshyperbolicity. Numerical results are shown on a plane strain modeling of the Kalthoff-Winkler test.Ces travaux proposent un modèle hyperbolique d’endommagement à gradient destiné au calcul numé-rique explicite efficace des problèmes de rupture fragile dynamique en petites déformations. En sui-vant la méthode du “Lagrangien étendue”, le problème de minimisation globale généralement formulépour l’endommagement à gradient est remplacé par un ensemble d’équations hyperboliques avec termessource purement local qui peut facilement être résolu par volumes finis. L’endommagement unilatéralest dans ce modèle introduit dans une décomposition sphérique/déviatorique de l’énergie qui garantiel’hyperbolicité. Le modèle est illustré sur une modélisation en déformation plane de test de Kalthoff-Winkler
Cavitation sous choc et interaction fluide-structure
No full textInternational audienceCavitation sous choc et interaction fluide-structur
Les outils traditionnels au service de la protection des acteurs économiques face au numérique (volet 2)
No full textInternational audienc
Plastics used in agriculture and for food: uses, properties and impacts. Condensed report of the collective scientific assessment
No full textLa responsabilité des autorités infra-étatiques et le droit de l'Union européenne de la protection des données personnelles.
No full textInternational audienceLa gouvernance à multiniveaux, déployée par l’Union européenne et impliquant de manière croissante les autorités infra-étatiques dans la mise en œuvre du droit et de l’action de l’Union européenne, combinée à l’essor de l’administration dématérialisée, expose directement les autorités infra-étatiques à des obligations en matière de protection des données personnelles. L'étude de la jurisprudence récente de la Cour de Justice de l’Union européenne permet de démontrer que les interprétations extensives des notions de données personnelles, de traitement et de responsable du traitement de données amplifient la responsabilité des autorités infra-étatiques dans la mise en œuvre du droit de l’Union européenne, ce qui peut les placer en difficulté, notamment financière, du fait de la dualité du régime de sanction incluant la nécessaire réparation du préjudice moral
